This invention relates to a method and apparatus for controlling the temperature of oil maintained in an overhead tank. More specifically the invention concerns rerouting oil being supplied to the seals of a turbomachine to direct a portion of the oil through an overhead tank to maintain the overhead tank oil temperature at a desired level.
Large turbomachines utilize oil seals which prevent gases from escaping along the shaft ends to the environment. Typically these seals are provided with an oil supply system which supplies clean oil under pressure to the seals and receives contaminated oil from the seals. The oil delivery system typically includes a console which acts to supply oil under pressure and receives the discharged oil from the compressor. The console acts to clean and/or filter the oil, to increase or reduce its temperature, to remove pollutants therefrom by various processes and to otherwise condition the oil such that it may be resupplied to the turbomachine under pressure.
Seals used on large turbomachines do require oil for cooling and sealing. The interruption of the flow of oil for sealing purposes results in catastrophic failures. It is known to provide a back-up oil delivery system for maintaining oil flow under pressure to the seals in the event of failure of the oil supply system. It is further known to mount an overhead tank at a desired height containing oil to establish the proper seal differential pressure such that oil may be supplied from the tank to the seals under pressure to provide the necessary sealing on an interim basis.
The overhead tank is located at a height sufficiently above the turbomachine that a static pressure head is created therebetween such that the oil at the desired pressure may be supplied from the tank. The desired pressure level is required since oil must be maintained at a pressure slightly above the gas pressure to prevent leakage of the gas.
In certain plant layouts the overhead tank is mounted quite a distance from the turbomachine and often in an ambient of significantly different temperature conditions. Under these circumstances since the oil in the tank tends to be stagnant except when the tank is being filled or in an emergency situation requiring emptying of the tank, the oil in the tank tends to reach the ambient temperature condition. Should the oil in the tank be much cooler than the desired oil supply temperature, then the viscosity of the oil changes and the volume flow of the oil through the supply lines to the turbomachine may be reduced such that an emergency supply of oil is not provided when necessary. Again should oil of much lower viscosity be supplied thereto the volume flow of oil through the seals will be significantly reduced and the seals may be starved causing damage to the seals and effectively preventing the back-up emergency oil supply system from accomplishing its desired sealing function.
The solution proposed to the problem of the temperature of the oil in the tank not being at the desired operating temperature includes routing a portion of the oil being supplied to the turbomachine through the tank such that the oil in the tank is maintained at the desired operating temperature rather than the ambient temperature of the region where the tank is located. A specific supply system including level sensors and control valve for diverting a portion of the flow of sealing oil to the tank is set forth herein.